1. Field of the Invention
The present invention relates to a microactuator, a magnetic head device, and a magnetic recording apparatus, and more particularly, to the structure of a microactuator that is incorporated in a magnetic head device and that is suitable for use in finely adjusting the position of a magnetic head when the magnetic head is precisely positioned over a track on a magnetic recording medium.
2. Description of the Related Art
A typical magnetic recording apparatus includes a magnetic recording medium having a data recording surface, such as a magnetic disk, and comprises a magnetic head for writing on and reading information from the magnetic recording medium, a head support section for supporting the magnetic head, including a slider, a gimbal, and the like, a head driving section, such as a voice coil motor, for driving the support section to position the magnetic head with respect to a predetermined track on the magnetic recording medium, and the like. Even when the voice coil motor operation is very precise, however, the positioning of the magnetic head only by the voice coil motor limits positional accuracy, especially for finer track widths. Accordingly, a method has been proposed in which the head position is finely adjusted by using a precise actuator after coarse adjustment by a voice coil motor.
FIGS. 25 and 26 show an example of a conventional high-precision actuator that is capable of micromovement. An actuator 101 shown in FIGS. 25 and 26 uses electrostatic attractive force as the driving force, and is generically referred to as an xe2x80x9celectrostatic actuatorxe2x80x9d. In the electrostatic actuator 101, two substrates, a first substrate 102 and a second substrate 103, are spaced opposed to each other so as to allow relative motion. A first comb-like electrode 104 having a plurality of parallel teeth 104a is formed on a surface 102a of the first substrate 102 facing the second substrate 103, and a second electrode 105 having a plurality of parallel teeth 105a, which are placed between the adjoining teeth 104a of the first electrode 104, is formed on a surface 103a of the second substrate 103 facing the first substrate 102.
In the electrostatic actuator 101 having the above-described configuration, when voltage is applied between the first electrode 104 and the second electrode 105, electrostatic attractive force is generated therebetween, and causes the first substrate 102 and the second substrate 103 to move relative to each other so that the first electrode 104 and the second electrode 105 approach in a direction such that the degree of engagement increases between the first electrode teeth 104a and the second electrode teeth 105a. After that, when the voltage is cut off, since the electrostatic attractive force disappears, the first substrate 102 and the second substrate 103 move relative to each other so that the first electrode 104 and the second electrode 105 separate in the direction opposite from that at the time of voltage application, that is, in a direction such that the degree of engagement decreases between the first electrode teeth 104a and the second electrode teeth 105a. 
As described above, the electrostatic actuator is driven by electrostatic attractive force generated between two substrates. A detailed description will be now given of the electrostatic attractive force between the substrates. It is believed that a force F1 acts to increase the area of the opposing portions of the faces of the first electrode and the second electrode in parallel to the direction of relative motion between the substrates when voltage is applied, and that a force F2 acts so that approaching and separating faces of the first electrode and the second electrode attract each other when voltage is applied. An electrostatic attractive force F serving as the driving force is the resultant of F1 and F2. The forces F1 and F2 are given by the following expressions, respectively:
F1=(xcex50xc2x7V2xc2x7t)/g1xe2x80x83xe2x80x83(1)
F2=(xcex50xc2x7V2xc2x7S)/g22xe2x80x83xe2x80x83(2)
where xcex50 is the dielectric constant of a vacuum, g1 is the distance between the faces of the electrodes in parallel with the direction of relative motion between the substrates, t is the electrode thickness, S is the area of the approaching and separating faces of the electrodes, and g2 is the distance between the approaching and separating face of the electrodes.
In a case in which the first electrode and the second electrode are placed somewhat apart from each other, F1 is generally dominant because F2 significantly decreases.
When it is assumed that the driving force F is equal to F, the dielectric constant xcex50 of a vacuum and the electrode thickness t are constant, and the distance g1 between the faces of the electrodes parallel to the direction of relative motion between the substrates remains constant even when the electrodes move relative to each other. Therefore, the driving force F varies only according to the voltage V between the electrodes. For example, when this electrostatic actuator is adopted in a magnetic head device to finely adjust the head position, the substrate moving distance is controlled by controlling the driving force through the adjustment of the voltage between the electrodes. Therefore, it is necessary to previously take into consideration the relationship between the voltage and the driving force and the relationship between the driving force and the moving distance in individual actuators. Furthermore, there is a need for a system for controlling the substrate moving distance, including a voltage adjustment mechanism, which is relatively complicated. In particular, a conventional device requires a complicated moving distance control system in order to achieve stepwise micromovement, and there has been a demand for an electrostatic actuator that can simplify such a control system.
The present invention has been made to solve the above problems, and it is accordingly an object of the present invention to provide an electrostatic microactuator that can simplify a system for controlling the moving distance, compared with the conventional microactuator, and a magnetic head device and a magnetic recording apparatus using the microactuator.
In order to achieve the above object, according to an aspect of the present invention, there is provided a microactuator wherein opposing substrates are spaced so as to move relative to each other, and a plurality of actuators for providing different distances of relative motion between the substrates are arranged between the substrates at predetermined intervals in the direction of relative motion between the substrates.
Although microactuators having a plurality of actuators to produce a strong driving force have been known hitherto, the actuators provide the same relative moving distance, and a complicated system is needed to control the relative moving distance. In contrast, since a plurality of actuators, which provide different relative moving distances are arranged between the opposing substrates in the microactuator of the present invention, only the actuator that provides a required relative moving distance can be operated, which makes it possible to change the relative moving distance of the substrates in a stepwise manner without using any complicated control system.
In a specific structure in which a plurality of actuators are provided to provide different relative moving distances, each of the actuators comprises a first comb-like electrode formed on the opposing face of the first substrate, and having a plurality of parallel teeth aligned at the leading ends thereof; and a second electrode formed on the opposing face of the second substrate, and having a plurality of parallel teeth aligned at the leading ends thereof so as to be placed between the adjoining teeth of the first electrode and to extend outside the leading ends of the teeth of the first electrode in an undriven state, the outer ends of the extending portions of the plurality of teeth being moved to the leading ends of the teeth of the first electrode in a driven state in order to cause the substrates to move relative to each other. The outside extending portions of the second electrode teeth are different in length among the actuators.
In the case of the above-described conventional electrostatic microactuator, an electrode pair formed by the first electrode and the second electrode can be regarded as an actuator. The driving force F1 in the faces of the first electrode and the second electrode in parallel with the direction of relative motion between the substrates acts to increase the opposing area of the faces when voltage is applied. In this case, the maximum relative moving distance of the substrates is determined by the length (area) of the portions of the second electrode teeth that extend outside the leading ends of the first electrode teeth in an undriven state. Therefore, when the extending portions of the second electrode teeth are made different in length among the actuators, it is possible to achieve a structure in which a plurality of actuators are provided that provide different relative moving distance of the substrates. Even when the same voltage is applied to the actuators, as long as the voltage is set at a sufficient voltage to obtain the maximum relative moving distance in a driven state, the relative moving distance of the substrates differs among the actuators.
In other words, the conventional microactuator adjusts the moving distance by controlling the voltage to be applied between the electrodes, whereas the microactuator of the present invention adjusts the moving distance by switching among a plurality of actuators. Therefore, according to the microactuator of the present invention, there is no need to adjust the applied voltage in order to control the moving distance of the substrates.
In the microactuator of the present invention, it is preferable that approaching and separating faces of the first electrode and the second electrode, which are opposed to each other, not be parallel. The xe2x80x9capproaching and separating facesxe2x80x9d mean opposing faces of the first and second electrodes that approach or separate when the first and second electrode move relative to each other with the movement of the substrate.
As described above, in the conventional electrostatic actuator including the first comb-like electrode having a plurality of teeth and a second electrode having a plurality of teeth that are placed between the adjoining teeth of the first electrode, the force F2, by which the approaching and separating faces attract each other of the first and second electrodes, acts when the first electrode and the second electrode approach at the time of voltage application. According to the present invention, since the opposing approaching and separating faces of the first electrode and the second electrode are not parallel to each other, the force F2 can be thereby reduced. This results in a reduced influence of F2 that tends to rapidly increase with the approach of the electrodes, and the total electrostatic attractive force, namely, the driving force F can be made more constant, compared with the conventional actuator.
In order that xe2x80x9cthe opposing approaching and separating faces of the first electrode and the second electrode are not parallel to each otherxe2x80x9d, as described above, for example, (1) both the opposing approaching and separating faces of the first electrode and the second electrode are convexly shaped to taper off toward the end, (2) the approaching and separating faces of one of the first and second electrodes are concavely shaped to broaden toward the end, and the approaching and separating faces of the other electrode are made flat, or (3) the approaching and separating faces of one of the first and second electrodes are convexly shaped to taper off toward the end, and the approaching and separating faces of the other electrode are made flat. In order to give priority to the advantage of the constant driving force F, the form (1), in which both the electrodes do not include flat faces, is the most preferable, and the forms (2) and (3) are equivalent to each other.
Since a substantial driving force F can be obtained, the preference increases in the following order: the form (2) including concave faces broadening toward the end and flat faces, the form (3) including convex faces tapering off toward the end and flat faces, and the form (1) including convex faces tapering off toward the end, although this slightly impairs the advantage of making the driving force F constant.
The substrates that are constituents of the microactuator of the present invention may be made of, for example, a glass substrate, a glass-nickel-glass laminate substrate, or a silicon-nickel-glass laminate substrate. The electrodes may be made of, for example, silicon having conductivity, and may be adhered to the glass substrate. As will be described in detail later, an actual microactuator requires, in addition to the substrates and electrodes, a component that functions as a spring for moving the substrates relative to each other in a direction such that the teeth of the electrodes approach when voltage is applied, and for subsequently returning the substrates to the position before the voltage was applied when the voltage is cut off. In this case, the spring portion may be made of silicon, and may be subjected to working together with the electrodes. Furthermore, wires for applying voltage to the electrodes may be formed of metal, such as aluminum or platinum-titanium, on the substrates. Since there is a need to switch among the actuators in the present invention as necessary, the actuators must individually include wires for voltage application.
According to another aspect of the present invention, there is provided a magnetic head device including the above-described microactuator.
According to a further aspect of the present invention, there is provided a magnetic recording apparatus including the above magnetic head.
That is, the use of the microactuator including a plurality of actuators, which provide different working amounts, as described above, permits stepwise operation for finely adjusting the position of the magnetic head with respect to a predetermined track on a magnetic recording medium. The magnetic head device and the magnetic recording apparatus can control the shift amount of the microactuator by only employing a simple switching means, such as a switch, without using a complicated shift amount control system for the microactuator. This can make the device configuration simpler than before.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.